Admittance of a long diffusive SNS junction

TL;DR

This paper investigates the admittance of long diffusive SNS junctions in the linear response regime, revealing new behaviors of the dissipative part near the minigap closing, especially in different temperature regimes.

Contribution

The study provides a detailed calculation of the admittance using Usadel equations, highlighting qualitative differences in behavior across various temperature and frequency regimes.

Findings

ReY(ω) peaks at phase difference π when the minigap closes.

Behavior differs significantly between high and low temperature regimes.

Dissipative response persists even when supercurrent is suppressed.

Abstract

The dynamical properties of hybrid normal metal/superconductor structures have recently come into research focus both experimentally and theoretically. Recent experimental studies of the coherent admittance $% Y(\omega )$ of SNS rings as function of the phase difference $\phi _{0}$ are still not fully understood. Here we concentrate on the linear response regime, calculating $Y(\omega )$ by solving Usadel equations, linearised in electric field. Although partially reproducing previously known results, we find qualitatively different behaviour in the collisionless regime of $\tau _{in}^{-1}\ll \omega \lesssim E_{Th}$ and high temperature $T\gg E_{Th}$ and low temperature $T\lesssim E_{Th}$ near the minigap closing $\phi _{0}\sim \pi $. We find that the dissipative part $\mbox{Re}Y(\omega )$ peaks when the minigap closes (at a phase difference of $\pi $) even at high temperatures, when the equilibrium supercurrent is fully suppressed.